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Physiology > Microcirculation > Flashcards

Microcirculation Flashcards

1
Q

What are the two types og substance exchange in Micorcirculation?

A
  1. diffusion

2. filtration/resorption (Starling forces)

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2
Q

What do the two types of material exchange in the microcirculation determine?

A

The rate of delivery of nutrients to the tissues and the rate of the metabolite transport from the tissues.

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3
Q

What happens if the precapillary sphincter is closed?

A

There is no filtration, but resorption is possible.

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4
Q

Morphology of the Microcirculation:

A

Arterioles (+- 20um) –> then metarterioles (rich in smooth muscle) –> precapillary sphincters –> Capillaries
- Capillaries are running into venules, then veins carry the blood back to the heart.

  • Some shunts also exist between arterioles and venules (creating arteriovenous anastomosis)
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5
Q

How many % of the capillaries are open during rest?

A

5-10%

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6
Q

Microcirculatory bed gives also room for?

A

Dead-end lumph vessels, collecting surplus EC fluid into the circulation.

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7
Q

Materials needed for Exchange of substances during diffusion

A
  • gas exchange
  • water/ion exchange
  • small substances
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8
Q

What are the types of Exchange of substances with diffusion?

A
  • Flow limited (small substances)

- Diffusion limited (bigger molecules)

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9
Q

What are the factors influencing diffusion?

A
  • Concentration gradient
  • Permeability
  • surface of the capillary
  • time available for the diffusion
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10
Q

The extent of gas diffusion depends on?

A

Partial Pressure

- that drops towards the end of the capillary and toeards the distant cells.

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11
Q

What happens with higher O2 consumption of a tissue?

A

The faster the drop of the pO2 will be (partial pressure oxygen)
- This will lead to hypoxia

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12
Q

What does Hypoxia mean?

A

It results in the involvment of more (resting) capillaries.
This local autoregulation is a very important way of insuring an even distribution of gases, and nutrients, in a tissue.

Hypoxia happens when the O2 consumption of a tissue gets higher, which leads to faster drop of pO2.

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13
Q

What happens with the diffusion when there is higher need for O2 in the tissue?

A

Higher need for O2 in the tissue, faster the blood flow, so the average time spent in the capillary will be too short for optimal gas-exchange.
- that lack of O2 turns on regulatory mechanisms, mo more capillaries will be connected into the microcirculation, more sphincter will open, larger capillary space will be active.

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14
Q

What is Partial Pressure?

A

It is the individual pressure exerted independently by a particular gas within a mixture of gases.

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15
Q

What are the major forces (Starling forces) of the Exchange of Substances with Filtration/Reabsorption?

A
  • Hydrostatic pressure difference (Ph)
  • Permeability
  • The oncotic pressure (Ponc)
  • The pressure of the surrounding tissue (Pinterst)
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16
Q

What is the Effective Filtration Pressure?

A

It determines the direction of the substance movement

17
Q

The Direction of plasma flow equation?

A

Peff = (Ph.capill - Ph.interst) - (Ponc.capill - Ponc-interstit) - Pinterst

18
Q

Oncotic pressure is?

A

constant in the capillary

19
Q

Hydrostatic pressure is?

A
  • constantly dropping to the venous end of capillary
  • Hydrostatic pressure is lower in the capillary than in the artery, and gradually decreases while the blood flows through the capillary.
20
Q

What happens if the hydrostatic pressure is higher than the oncotic?

A

= Net filtration

21
Q

What happens if the hydrostatic pressure is lowerthan the oncotic?

A

= net reabsorption

22
Q

How do Osmotic pressure occur?

A

The wall of the capillary is permeable for water and impermeable for plasma proteins, hence the macromolecules generate osmotic pressure.

23
Q

What is the Gibbson-Donnan effect?

A

The plasma proteins are negatively charged, therefore they try to keep cathions within the plasma –> so they increase the osmotic gradient between the plasma and the interstitial space.

24
Q

What is the sucking force?

A

The combination of the osmotic force and the Gibbs-Donnan effects generate suckng force, which absorb H2O form ISF to the plasma

This is called Colloid Oncotic pressure

25
Q

Oncotic pressure is proportional with?

A

The protein concentration of plasma and of the ISF

26
Q

Describe the veins

A
  • Function: reservoir
  • Resistance is zero
  • Distended by increased pressure
  • Enlargement is limited by collagen fibers
27
Q

What type of Venule types exist?

A
  • Postcapillary venule (some pericytes)
  • Collecting venule (continous pericyte layer)
  • Muscular venule (contractile elements are present)
28
Q

What are characteristics of the venous system?

A
  1. Capacitance system (reservoir)
  2. Redistribution:
    - the vasomotor mechanism, sympathetic vasoconstrictor through alpha-receptors, may redistribute blood toward the resistance segment.
  3. Distensibility is large
    - but the collagen network sets the limit.
29
Q

Function of the Venous circulation is determined by?

A

Structure of the wall of venous valves

30
Q

Pressure and flow rate change with certain rhythm in the veins due to?

A

Due to the valves and change of tissure pressure (i.e muscle pump) and gravitation

31
Q

The maintenance of venous blood flow is determined by?

A

By the work of the heart and gravitation and pressure.

32
Q

Factors maintaining the venous blood pressure:

A
  • “Vis a tergo” the work of the heart (force from behind)
  • Gravitation
  • Venous valves
  • Skeletal muscle pump
  • Changing pressure in chest and abdomen
  • CVP
33
Q

What is the Central Venous Pressure (CVP)?

A
  • Pressure in the RA and in the hollow veins is normally 0mmHg. due to the cardiac cycle, positive pressure changes can be detected in the RA (= CVP)

Physiology (11 decks)

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